Endovascular therapy has been used in treating a variety of conditions, such as in controlling internal bleeding, occluding blood supply to tumors, and relieving vessel-wall pressure in a region of a vessel aneurism (Athanosoulis, Wallace, Reuter).
The embolic agent may be an injectable fluid, such as a microfibrillar collagen (Battista, Kaufman, Kumar), Gelfoam (Berenstein, Roberson) silastic beads (Hilal), and polyvinyl alcohol foam (Latchaw). Co-owned U.S. patent application Ser. No. 823,635 describes a cross-linked vaso-occlusive agent whose persistence at a vaso-occlusive site can be extended up to several months, depending on the degree of cross-linking. These fluid agents can be injected into a selected vessel site through a catheter, and there gel into a solid, space-filling mass at the injection site. Typically such fluid agents provide good short-term vaso-occlusion, but are ultimately resorbed in the process of vessel recanalization.
Polymer resins, such as cyanoacrylate resins, have also been employed as an injectable vaso-occlusive material. Like injectable gel materials, the resins are typically mixed with a radiocontrast material in order to be seen fluoroscopically. A risk with this material is inadvertent embolism in normal vasculature due to the inability to control the destination of pre-gelled resins. The material is also difficult or impossible to retrieve, once placed.
Two types of mechanical vaso-occlusion devices are known. The first is a balloon which can be carried to the vessel site at the end of a catheter, and there inflated with a suitable fluid, typically a polymerizable resin, and released from the end of the catheter. The balloon device has the advantage that it effectively fills the cross section of the occluded vessel. A vascular balloon is difficult or impossible to retrieve after the resin in the balloon sets up, and the balloon cannot be visualized unless it is filled with a contrast material. Also the balloon can rupture during filling, or release prematurely during filling, leaking monomer resin into the vasculature.
A second type of mechanical vaso-occlusive device is a wire coil which can be introduced through a catheter in a stretched linear form, and which assumes a helical wire shape when released into a vessel. In vaso-occlusion coils used heretofore, the wire itself is a relatively stiff, shape-retaining stainless steel coil. The wire is shaped to have 1-2 helical windings dimensioned to engage the walls of the vessel. The wire is also coated with filaments, such as dacron or cotton fibers, which provide a substrate for clot formation in the interior region of the vessel, while the coil itself serves to anchor the device on the vessel wall at the site of release. This type of coil is also known as a Gianturco coil (Cook Corp, Bloomington, Ill.). The coil is relatively permanent, can be imaged radiographically, can be located at a well-defined vessel site, and has the possibility at least of being retrieved. A limitation of fibercoated coils is that recanalization of the vessel can occur, presumably by resorption of the clot by endothelial cells. Further, the fiber-coated coils are difficult to introduce into vessel sites which require tortuous path access and/or involve vessel size less than about 1-3 mm. This is because a fiber-coated coil is generally too stiff and has too high a frictional coefficient to be readily advanced through a small-diameter catheter, especially in a region of catheter bends.